1. Field of the Invention
The present invention relates generally to vehicle navigation apparatus and, more particularly, to automatic re-search used when the vehicle strays from a predetermined route.
2. Prior Art
Conventional vehicle navigation systems are designed to search map and road data to determine an optional or "guidance route" to a destination, responsive to input of a destination, a pass-through location, a stop-over point and the like, and to provide guidance along the determined guidance route. Generally, such systems include a function for renewed automatic searching or "re-searching" responsive to determination that the vehicle has deviated from the guidance route. In the automatic researching mode, when it is detected that the present vehicle location is off of the guidance route, a search is made either (1) to determine an entire new route extending all the way to the destination or, alternatively, (2) to determine a route returning to the original guidance route by a search of road information limited to an area near or around the present position.
The first type search, i.e. for an entire new route to the destination, when the vehicle departs from the guidance route, requires much time to complete. In order to reduce the search time, some conventional systems are designed to conduct the second type search, i.e. for a route returning at the original route limited to road information for the nearby area around the present vehicle location. However, this latter system is more likely to settle on a route at odds with the drivers' intentions and/or preferences or on a route requiring travel a long distance out of the way, because of the fact that it seeks a return to the original route.
Conventional vehicle navigation apparatus permits input of a destination, pass-through point, facility to see, and the like, searches for a guidance route to a destination, and outputs guidance during travel along the route determined by the search. Typically, such apparatus displays on a guidance screen marks representing facilities (landmarks) such as gas stations, banks, convenience stores, and the like. Another navigation apparatus which has been proposed is capable of offering selectivity with respect to landmarks to be displayed on the guidance screen. For example, such a navigation apparatus may be designed so that in cases where an immediate stop at a nearby gas station is required due to shortage of vehicle fuel, it displays marks representative of gas stations thereby enabling a vehicle driver to find the nearest gas station. In displaying such landmarks by the prior art navigation apparatus, there has been the problem that where a great number of facilities are present as landmarks within an area being displayed on the guidance screen, if these are displayed automatically, the original map on which such landmarks are superimposed becomes difficult to see.